Technical Field
The present invention relates to a semiconductor device and a semiconductor device manufacturing method.
Background Art
An insulated gate field effect transistor (hereinafter, referred to as a SiC-MOSFET) has been known as a semiconductor device using a silicon carbide (SiC) semiconductor. A representative example of the front surface element structure of the SiC-MOSFET includes a MOS gate (metal-oxide film-semiconductor insulated gate) structure having a silicon dioxide (SiO2) film as a gate insulating film, a phosphosilicate glass (PSG) film as an interlayer insulating film, and an aluminum (Al) electrode as a front surface electrode, which are provided on the front surface side of a SiC substrate.
The structure of the SiC-MOSFET according to the related art will be described with reference to FIG. 16. FIG. 16 is a cross-sectional view illustrating the structure of the SiC-MOSFET according to the related art. As illustrated in FIG. 16, the SiC-MOSFET according to the related art includes a MOS gate structure including a p base region 103, an n++ source region 105, a p+ contact region 106, a gate oxide film 108, and a gate electrode 109, an interlayer insulating film 110, and an aluminum-silicon (Al—Si) electrode 113, which are provided on the front surface side of an epitaxial substrate obtained by depositing an n− epitaxial layer 102 on the front surface of a SiC substrate 101.
The interlayer insulating film 110 has a source contact hole through which the n++ source region 105 and the p+ contact region 106 are selectively exposed. The Al—Si electrode 113 is provided so as to cover the front surface of the substrate in an active region and is electrically connected to portions of the n++ source region 105 and the p+ contact region 106 which are exposed through the source contact hole of the interlayer insulating film 110. In addition, the Al—Si electrode 113 is electrically insulated from the gate electrode 109 by the interlayer insulating film 110. Reference numeral 104 indicates a p epitaxial layer and reference numeral 107 indicates an n inversion region. Reference numeral 111 indicates a titanium nitride (TiN) film and reference numeral 112 indicates a nickel (Ni) film.
A contact metal film 114 and a rear surface electrode 115 are sequentially formed on the rear surface of the epitaxial substrate, that is, the rear surface of the SiC substrate 101. The SiC-MOSFET is mounted in a package and a bonding wire (not illustrated) made of aluminum is electrically connected to the Al—Si electrode 113, which is the front surface electrode, and an external connection terminal by ultrasonic vibration. A metal film is formed on the surface of a portion of the Al—Si electrode 113 to which the bonding wire is connected. In this way, instead of the Al—Si electrode 113, solder is closely adhered to a lead frame having copper (Cu) as a base material.
As a method for forming the metal film on the surface of the front surface electrode, a method has been proposed which continuously performs a step of bringing the material to be plated into contact with an electroless gold plating solution without gold ions and a step of bringing the material to be plated into contact with an electroless gold plating solution including gold ions (for example, see JP 2000-223442 A). In addition, as another method, a method has been proposed which performs plating on a conductive portion that is formed on the surface of a substrate to sequentially form a Ni film having Ni as a main component and an Au film having gold (Au) as a main component and performs post-processing for removing a Ni compound attached to the surface of the Au film (for example, see JP 2004-107734 A).
As still another method, a plating method has been proposed which forms a first metal film made of Ni—P (phosphorus) on a metal film using a plating process and forms a second metal film having Au as a main component on the first metal film using the plating process (for example, see JP 2006-131949 A). In this plating method, a first Ni plating solution which is used to form the first metal film with a P content of 3 wt % to 6 wt % is produced and a second Ni plating solution which is used to form the first metal film with a P content of 6 wt % to 9 wt % is produced. The first Ni plating solution is used to form the first metal film as a first layer on the surface of the metal film. Then, the second plating solution is used to form the first metal film as a second layer.